Oscillograph



April 7,19 2- 2 w. H. MAYNE 2,219,124

OSCILLOGRAPH Filed June 24, 1941 z/ELE.

Patented Apr, 7 1942 v William H. Mayne, San Antonio, Tex

Olive 8. Petty, San Antonio,

alsignor to Tex.

Application-June 24, 1941, Serial No. 399,549 6 Claims. "(CL 111-95) This invention relates to improvements in oscillographs, especially instruments of the multiple string type. It is the primary object oi the invention to minimize distortion of the record produced by such instruments as the result of undesirable string vibrations.

More specifically, it is an object of the invention to confine the strings to movement in prescribed paths such as will ensure freedom from 'tangling or collision and to control string dis-' placement by adequate and effective damping.

The invention is illustrated as applicable to a multiple string galvanometer of the Einthoven type in which a plurality of strings are supported in parallel relation in a magnetic field, and in sensitized sheet, is intercepted by the strings so that string vibration resulting from varying flow of current in the strings may be recorded. It is" customary in such instruments to concentrate the magnetic field adjacent the strings by the use of pole pieces, and it is desirable to incline the faces ofthe pole pieces at an acute angle with respect to the plane of the strings, so that the strings will not tangle or collide even though disposed in closely contiguous relation. It is a feature of the invention that these pole pieces are offset in the direction of a normal to the strings lying in the plane of the strings, in order that the end strings of the series will not collide with or tangle with the ends of the pole pieces when vibrating in planes normal to the magnetic field.

It is a further object of the invention to control the vibration of the strings by the provision of effective electrical damping. To this end, the resistance of the circuit containing the string is minimized by the provision of a suitable shunt for the usual tensioning spring, and the pole pieces are so dimensioned with respect to the length of the string, and the light beam so projected across the spring, as to minimize distortion resulting from modes of vibration other than the fundamental.

Further objects and features of the invention which a beam of light, projected on a moving tensioning spring and associated shunt shown in gure 1;

Figure 4 is an enlarged sectional view of the pole pieces shown in Figures 1 and 28;

Figure 5. is a diagrammatic view similar to Figure 4 and illustrating the disposition of the magnetic lines of force between the pole pieces; and

pole pieces are not ofiset.

In order to facilitate an understanding of the invention, reference will be made to the several embodiments thereof illustrated in the accompanying drawing and specific language will be employed. It will nevertheless be understood that various further modifications of the devices illustrated herein, such as would fall within the province of those skilled in the art to construct. aire contemplated as part of the present invent on.

that the oscillograph strings it are illustrated as mounted in a supporting frame ll. Each string is suitably tensioned by elastic means in the form of a. coil spring [2 which is mounted being formed of material of high conductivity,

for example copper. By this means the resistance in the string circuit, ordinarily substantially increased by the spring which is commonly will be apparent from the following description taken in connection with the. accompanying drawing, in which: v Figure 1 is an end elevation of the essential elements of an oscillograph constructed in ac-- cordance with the instant invention;

Figure 2 is a view taken substantially on the line 2-2 of Figure 1;

Figure 3 is an enlarged view of the string ployed so as to give an efiective D.

made of phosphor bronze, may be reduced to a minimum in order to increase the electrical damping of the string.

For example, in a typical case, the resistance of the string and of the spring may be five ohms each, making a total resistance without the shunt connection-of ten ohms. Thus 50% or the exciting energy is wasted in the spring. In order to obtain results which at least approach satisfactory efilciency with the ten ohm string and spring combination, the resistance of the external circuit should be at least thirty ohms. This means that the total D. C. resistance in the damping circuit will be forty ohms However, if the shunt connection across the spring is em- C. resistance Figure 6 is a view corresponding to Figure 5, illustrating the magneticlines of force when the Referring first to Figure 1, it will be observed .2. having energizing windings 2| acutely angled ends.

of five ohms in the string and shunted spring. the resistance of the external shunt can be reduced to fifteen ohms toaflord the same efiiciency; so that the in; circuit of the galvanometer is reduced from forty ohms to twenty ohms, with resultant doubling of the sensitivity as well as the damping. The magnetic field for the strings is preferably provided by an electromagnet comprising a core associated therewith. The field is concentrated in the neighborhood of the strings by means of pole pieces liwhichmaybeboltedtothecoreasatfl. The

strings I. are arranged in parallel relation in a common plane, and the faces 28 of the pole pieces define parallel planes which are inclined at an acute angle with respect to the plane of the strings. This is desirable, as has been heretofore recognized. since the individual strings are thereby. caused to vibrate in planes substan-' tiallyparallelto thepolefacesandmay thusbe arranged much more closely without risk of collision or tangling, with consequent increase in compactness and reduction in cost of the optical system associated with the instrument.

The sides of the pole pieces are tapered in the direction of the strings; in'the embodiment of the invention shown, the inclination of the two sides of each pole piece tothe base thereof is of the order of 72 and 65 respectively.j It has been found that if this taper is too great the magnetic fiux leakage is excessive, whereas if the taper is too slight, the magnetic fiux is reduced total resistance in the dampby the resultant decrease in area-of'thepole pieces. The taper is accordingly selected. so as to afford minimum leakage and maximumfiux,

having due regard to other factors, such as the permeability of the metal of the pole pieces at various flux densities, and the size of the gap between the pole pieces.

As is apparent from Figures 2,4, ends, the

pole pieces are oifset in the direction of,- a normal to the strings lyingin theplaneof the strings, this feature being important to avoid tansling of the end strings with the pole pieces on the occurrence of vibration of large amplitude. Thus it will be' noted from Figure 5 that by oilsetting the-pole pieces to a suiiicientextent, the lines of magnetic force may be'so directed that and-it will be appreciated that since the. strings tend to move at right angles to the lines'of force, and the lines adjacent the ends of the pole pieces are decidedly curved, the outermost strings will tend to move toward and aroundthe-adiacent pole piece ends. 1

In this connection it will be observed that by reason of the inclination of the pole pieces, that end of each pole piece which is closestto the strings presents the more acute angle between the pole face and the side of the pole piece, and the pole pieces are therefore oifset'ins'uch adirection that these more acutely angledends proiect further beyond the strings than, do-.the less I have found that it is important in preventing distortion of the record as the resultjof harmonic vibrations that the depth of thepole faces.

as measured in the direction of the lcns should bear a ratio to the string length of the order of 5:9. This ratio is found to give the opdamping for the fundamental, while not materially reducing the damping of the third harmonic of the'string. The effect of second harmonic vibrations are eliminated by so positioning the string that the effective centertiiereof intercepts the light beam.

The optical means for producing the light beam is not shown herein but may assume any conventional form. The light is projected through bores 32 in the bases of the pole pieces and through slots 33 formed in the pole faces and extending into the pole pieces for a depth sufficient to provide uniformity of the magnetic field for the several strings.

It will be appreciated that while the invention is especially applicable to instruments of the multiplestring type, certain features thereof are useful in connection with instruments having I-Iavingthus described the invention, what is claimed as new and desired tobe secured by Let ters Patent; is;

1. In an oscillograph,the combination with a plurality of parallel oscillograph strings defining a common plane, of means establishing aAmagnetic field transversely of the strings, said means including opposed pole pieces having parallel faces disposed at an acute angle to the plane of the strings. said pole faces being oflset in, the dllLction of a normal to said strings lying in said p e.

2.1a an oscillograph, the combinationwith a plurality-of parallel oscillograph strings defining a commoniplane, of means establishing a magnetic field transversely of the strings, said means including opposed pole pieces having parallel faces disposed at an acute angle to the plane of the strings, the angle formed by each pole face with that sideof the pole piece which is closest to theplane of the strings being the more acute, said polefaces being offset in the direction of a normal to said strings lying in said plane, the more acutely angled sides of the respectiveipole pieces being disposed further beyond the strings.

3. In an oscillograph, the combination with a I plurality of parallel oscillographstrings defining timum results in the damping of vibrations of a common plane, of means'establishing a magnetlc field transversely of the strings, said means faces 'at an acute angle to the plane of the strings, said pole faces being offset in thedi-- rection of a normal to said strings lying in said plane, said pole faces having a depth, measured in the directionof the string length. such that the j ratio of the depth to the string length is of the order of 5:9.

. 4. In an oaciilograph, the combination with a plurality of parallel 'oscillograph strings defining a common plane, of means establishing a magnetic field transversely of the strings, said means including opposed pole pieces having parallel faces disposed at an acute angle to the plane of the strings, said pole faces being offset in the direction of a normal to said strings lying in said plane, a support for said strings. spring means the first and third orders, resulting adequate 7c connecting each of said strings to-said sup ort to tension the strings, and means or high conductivity arranged in shimt with each of said springs to reduce the electrical resistance 0! the string circuit. v

5. In an oscillograplnthe combination with a plurality of parallel oscillograph strings defining a common plane, oi'means establishing a magnetic fleld transversely oi the strings. said means including opposed pole pieces having parallel faces, said pole faces having a depth, measured in the direction of the string length, such that the ratio of the depth to the string length is 01' the order 01' 5:9.

' a common plane, or means establishing a magnetic field transversely of the strings, said means including opposed pole pieces having parallel faces, said pole faces having a depth, measured in the direction of the string length, such that the ratio of the depth to the string length is of the order 01' 5:9, and means projecting a light beam transversely of the plane of the strings and substantially at the mid-point of the string length.

WILLIAM H. MAYNE. 

